Online services such as web search and advertising are becoming increasingly personalized. The more and the longer a service knows about an individual, the better personalization it can provide. Typically, these online services build user profiles (containing, for example, web sites frequently visited, user interests, demographics information, location and so forth) on a server by tracking multiple online activities from the same user and linking them together using various techniques, usually under poorly informed user consent.
The simplest way to link a user's online activities is to use the Internet Protocol (IP) address of his device. However, as a device's IP address can change over time, online services track users across their IP sessions using cookies, device fingerprinting, and browser plug-ins, to name a few. To limit such tracking, users can hide IP addresses by using techniques such as, for example, proxies and anonymity networks or onion routing. They can also disable web cookies, and browse in private mode to prevent tracking by cookies. However, these approaches deny personalization because services do not have access to the information necessary for building user profiles anymore.